Crossword Puzzle Cause of lightheadedness?

Clue: Cause of lightheadedness?

Drop off at FedEx Office, perhaps (SHIP with 4 letters)
Ottawa official (GOVERNORGENERAL with 15 letters)
Office conference: Abbr. (MTG with 3 letters)
Officer's regular route (POLICEBEAT with 10 letters)
Ballpark officials (SCORERS with 7 letters)
Box-office smash (e.g. HIT with 3 letters)
Dinesen offerings (STORIES with 7 letters)
Broadcaster's ad offering (SPOTTV with 6 letters)
Tender offer, or what can be found seven times in this grid (TAKEOVERBID with 11 letters)
Encyclopedia offering (MAP with 3 letters)